We proceed to the third article thus:

1. It seems that God is not the same as his essence, or nature. Nothing can be in itself. But the essence or nature of God, which is his divinity, is said to be in God. God cannot then be the same as his essence or nature.

2. Again, an effect is similar to its cause, since every agent acts to produce its own likeness. Now with creatures, a subject is not the same as its essence. A man, for example, is not the same as his humanity. Neither then is God the same as his Divinity.

On the other hand: in John 14:6 it is clearly said that God is not merely living, but life: "I am the way, and the truth, and the life." Thus Divinity is to God as is life to one who lives. God is therefore Divinity itself.

I answer: God is the same as his essence, or nature. In order to understand this, we must realize that the essence or nature is bound to be different from the underlying subject where things are composed of matter and form, because their essence or nature comprises only what is included in their definition. [12] Thus humanity comprises what is included in the definition of man, or that by which a man is a man, and means that by which a man is a man. But the particular matter of the subject, and all the accidents which it possesses as an individual, are not included in the definition of the species. This flesh, these bones, whether the subject be white or black, and such things, are not included in the definition of man. Hence this flesh, these bones, and the accidents which distinguish this matter as individual are not included in the humanity, even though they are included in the man. The subject which is a man, therefore, included something which humanity does not include, so that a man is not precisely the same as his humanity. Humanity denotes the formal part of a man, since the defining principles are related to the individuating matter as its form. But where things are not composed of matter and form, and where individuation is not due to individual matter, that is, to this particular matter, but where forms individualize themselves, the forms are bound to be identical with the subsisting subjects, so that there is no difference between a subject and its nature. Now it was shown in the preceding article that God is not composed of matter and form. It follows that God must be his Divinity, and whatever else is predicated of him.

On the first point: we cannot speak of simple things except in terms of the composites by means of which we know anything. When we speak of God, therefore, we use concrete names to denote his substance, because only composite things subsist around us, and use abstract names to denote his simple nature. Hence when we say that Divinity, or life, or anything of this kind is in God, the compositeness belongs to the way in which our intellect understands, and not at all to that of which we speak.

On the second point: God's effects do not resemble him perfectly, but only in so far as they are able. Their likeness to God is deficient in that they can reflect what is simple and single only by what is many. They have the compositeness which necessitates the difference between a subject and its nature.

[12] Cf. Aristotle's distinction between "primary substance" and "secondary" substance," in Categories V, 2,1-5.